Quinacridone pigments in electrophotographic imaging

ABSTRACT

AN ELECTROPHOTOGRAPHIC PLATE INCLUDING A PHOTOCONDUCTIVE LAYER COMPRISING A NOVEL QUINACRIDONE PIGMENT IN A BINDER MATERIAL, SAID QUINACRIDONE PIGMENT HAVING THE FORMULA:   2,9-DI(R),3,10-BIS((2-R&#39;&#39;-PHENYL)-CO-NH-CH2-)-5,7,12,14-   TETRAHYDRO-QUINO(2,3-B)ACRIDINE-7,14-DIONE   WHEREIN R=CH3, C2H5,OCH3, OCH2H5 OR A HALOGEN AND WHEREIN R&#39;&#39;=AN AROMATIC, HETEROCYCLIC, ALICYCLIC OR ALIPHATIC GROUP IS DISCLOSED. METHODS OF PREPARING SAID PLATE AND OF USING SAID PLATE IN ELECTROPHOTOGRAPHIC PROCESSES ARE ALSO DISCLOSED.

w States Patentfimce 3,667,943

Patented June 6, 1972 tive. For this reason, selenium has been the mostcommer- Q MRWE 1N a; as; assassinate Y PHOTOGRAPHIC IMAGING LesterWeinberge'r, Penfield N.Y., assignor to Xerox aspects from l l hmltanonsm h Its Spectral Corporation Rochester, response is somewhat limited tothe ultra-violet, blue and No Drawing. Filed Aug. 22, 1968, Ser. No.754,726 green regwns of the spectrum and the p p o of Int. Cl, G03 5/06vitreous selenium plates requires costly and complex pro- U.S. Cl. 96-1PC 6 Claims cedures, such as vacuum evaporation. Also, vitreous seleniumlayers are only metastable in that they are readily 10 recrystallizedinto inoperative crystalline forms at tem- ABSTRACT OF THE DISCLOSUREperatures only slightly in excess of those prevailing in con Anelectrophotographic plate including a photoconducventionalelectrophotographic copying machines. Further, tive layer comprising anovel quinacridone pigment in a selenium plates require the use of aseparate conductive binder material, said quinacridone pigment havingthe substrate layer, preferably with an additional barrier layerformula; deposited thereon before deposition of the selenium photo- H HO o g N\ orrzNnb dNHoH 0 O I '7 g 2 R I N R -NH yo H J v C-NH-R' whereinR=OH C H ,OCH OC H or a halogen and conductor. Because of these economicand commercial .wherein R'=an aromatic, heterocyclic, alicyclic oraliconsiderations, there have been many recent efforts tophatic group isdisclosed. Methods of preparing said plate ward developingphotoconductive insulating materials and of using said plate inelectrophotographic processes other than selenium for use inelectrophotographic plates. are also disclosed. It has been proposedthat various two-component materials be used in photoconductiveinsulating layers used in electrophotographic plates. These consist of aphoto- BACKGROUND- OF THE INVENTION v conductive insulating material inparticulate form dispersed This invention relates, in general, toelectrophotography in an insulating binder. Where the particles consistof a and, more specifically, to a binder plate usable inelectrophotoconductive material comprising inorganic crystallinephotography. compounds containing a metallic ion, satisfactory photo- Itis known that images may be formed and developed graphic speed andspectral response for use in xerographic on the surface of certainphotoconductive insulating maplates are obtained. However, these plateseven when dyeterials by electrostatic means. The basicelectrophotosensitized generally have sensitivities much lower thanselegraphic process, as taught by Carlson in US. Pat. 2,297,- nium.These plates are generally considered to be non-re- 691, involvesuniformly charging a photoconductive inusable since it is necessary touse such high percentages sulating layer and then exposing said layer toa light-andof photoconductive pigment in order to attain adequate shadowimage which dissipates the charge on the portions sensitivity that it isdiflicult to obtain smooth surfaces of the layer which are exposed tolight. The electrostatic which lend themselves to efficient tonertransfer and sublatent image formed on the layer corresponds to theconsequent cleaning prior to reuse. An additional drawback in figurationof the light-and-shadow image. Alternatively, a the use of inorganicpigment-binder type plates is that latent electrostatic image may beformed on the plate by they can be charged only by negative and not bypositive charging said plate in image configuration. This image iscorona discharge. This property makes them commercially rendered visibleby depositing onthe imaged layer a finely undesirable since negativecorona discharge generates divided developing material comprising acolorant called much moreozone than positive corona discharge and is atoner and a toner carrier. The powdered developing magenerally moredifficult to control. terial will normally be attracted to thoseportions of the 1 It has been further demonstrated that organicphotolayer which retain a charge, thereby forming a powder conductivedyes and a wide variety of polycyclic comimage corresponding to thelatent electrostatic image. pounds maybe used together with suitableresin materials Where the base sheet is relatively inexpensive, such asto form photoconductive insulating layers useful in binderpaper, thepowder image may be fixed. directly to the plate type plates. Theseplates generally lack sensitivity levels as by heat orsolventfusing.Alternatively, the powder necessary for use in conventionalelectrophotographic image may betransferred to a sheet of receivingmaterial, copying devices. In addition, these plates lack abrasion suchas paper, and fixed thereon. The above general procresistance andstability of operation, particularly at eleess is also described in US.Pats. 2,357,809; 2,891,011; .vated temperatures.

and 3,079,342. In anothertype plate, inherently photoconductive poly-The photoconductive insulating layer to be elfective mers are usedfrequently in combination with sensitizing must be capable of holding anelectrostatic charge in the dyes or Lewis acids, to form photoconductiveinsulating dark and dissipating the charge to a conductive substratelayers. These polymeric organic photoconductor plates when exposed tolight. That variousphotoconductive ingenerally have the inherentdisadvantages of high cost of sulating materials may be used in makingelectrophotomanufacture, brittleness, and poor adhesion to supportinggraphic plates is known. Suitable photoconductive insulatsubstrates. Anumber of these photoconductive insulating ing materials such asanthracene, sulfur, selenium or mixlayers have thermal distortionproperties which make them vtures thereof havebeen disclosed by Carlsonin US. Pat. undesirable in an automatic electrophotographic appara-2,297,691.These materials generally have sensitivity in tus which oftenincludes powerful lamps and thermal fusthe blue or near ultraviolet,range, and all but selenium ing devices which tend to heat theelectrophotographic have a further limitation of being only slightlylight-sensiplate.

Thus, there is a continuing need for improved. photovaried over widelimits by selection of the appropriate reconductive insulating materialsfrom which stable, senslsins to suit specific requirements. In thisregard, these tive, and reusable electrophotographic plates can be made.photoconductive layers are superior to many heretofore SUMMARY OF THEINVENTION known binder suspensions of inorganic pigments which require arelatively high percentage of inorganic pigment It is, therefore, an obect of this invention to provide such that the inorganic pigment used ill cqntmls an electfophotogfaphlc Plate devold of the above'noted thephysical properties of the final photoconductive layer.

disadvantages. Since the percentage of quinacridone pigment needed isAnother object of this invention is to provide electror latively low,the photoconductive plate may have a Photographic Plates havingSensitivties which extend over very hard, very smooth surface. Thiseliminates many of Substantial Portions of the Visible P thedisadvantages of the prior pigment-binder plates which, Still anotherobject Of this invention is 1:0 provide a 1' 6- because f theproportions of igment had a very usable electrophotographic plate havinga high overall rough d abrasive f Sensitivity and high thermal StabilityWhen compared to While any of the novel class of quinacridones havingPresent commercially available reusable p the above-described generalformula may be used to pre- Yet aflflthaf Object of this invention is toProvide pare the photo-conductive layer of the present invention,photoconductive insulating material suitable for use in {Us preffirredto employ those i id h i R electrophotographic plates in both single useand reusable i l d f o h group consisting of CH (3 1-1 nd systems.mixtures thereof and wherein Yet another object of this invention is toprovide a photoconductive insulating layer for an electrophoto- RENE Ographic plate which is substantially resistant to abrasion and has arelatively high distortion temperature.

Yet another further object of this invention is to provide since thesematerials are highly photosensitive and proan electrophotographic platehaving a wide range of useful duce the most desirable images. physicalproperties. Various of the above-described novel quinacridones Theforegoing objects and others are accomplish d in may be utilized aloneor in combination with other comaccordance with this invention,generally speaking, by positions in any suitable mixture, dimer, trimer,oligomer, providing an electrophotographic plate having a novel polymer,copolymer or mixtures thereof.

photoconductive layer comprising a quinacridonc pigment The novel classof quinacridones of the persent invenin a resin binder, saidquinacridone pigment having the foltion are prepared by a method whichcomprises mixing a lowing general formula: compound having the .generalformula:

0 H g o R- HZNHJJ- l NHOH -R 001E 0 H g (I) 0 R oHlNnd--@ @Jinnon R Ii NR'NH0 t H CNH where R==CH C H OCH OC H or a halogen and where R=CH ,-C H001-1 OC H or a halogen, with R'-=an aromatic, alicyclic or aliphaticgroup. This particu- SOCl in 'dimethylformamide and then with 2R NH larclass of quinacridone pigments as well as methods for Where R"=anaromatic, alicyclic or aliphatic amine; their preparation are fully,described in copending'appli- Any suitable organic binder resin may beused in comcation, Ser. No. 754,634, filed in the U.S. Patent Oflicebination with the novel class of quinacridones to prepare Aug. 22,1968.the photoconductive layer of this invention. In order to Theabove-described quinacridone-resin photoconduc be useful the resin usedin the present invention should be tive layer may be deposited on anysuitable supporting submore resistive than about 10 and preferably morethan strate, or may be cast as a self-supporting film. The plate 10 ohmsper centimeter under the conditions of electromay be overcoated with anysuitable materials, if desired. photographic use. Typical resinsinclude: thermoplastics The quinacridone-resin photoconductive layer maybe including olefin polymers such as polyethylene and polyused in theformation of multi-layer sandwich configurapropylene; polymers derivedfrom dienes such as polytions adjacent a dielectric layer, similar tothat shown butyldiene, polyisobutylene, and polychloroprene; vinyl byGolovin et al., in the publication entitled A New and vinylidenepolymers such as polystyrene, styrene- Electrophotographic Process,Elfected by Means of Comacrylonitrile copolyrners, acryloru'trilebutadiene-styrene bined Electric Layers Doklady. Akad. Nauk SSSR vol. 55terpolymers, polymethylmethacrylate, polyacrylatcs, poly- 129, No. 5,pages 1008-1011, N overnber- December 1959. acrylics, polyacrylonitrilc,polyvinylacetate, polyvinyl It has been found that the percentage of theparticular alcohol, polyvinylchloride, polyvinylcarbazole, polyvinylclass of quinacridones described above which are required others, andpolyvinyl ketoncs; fluorocarbon polymers such to produce adequatesensitivity in a plate is very low. as polytetrafluoroethylene andpolyvinyldiene fluoride; Because of this, the mechanical properties ofthe photoconheterochain thermoplastics such as polyamides, polyesters,ductive layers are substantially determined by the proppolyurethanes,polypeptides, casein, polyglycols, polysulerties of the binder. A widevariety of resin binders may tides, and'polycarbonates; and cellulosicpolymers such as be used in the present invention, varying from softtherregenerated cellulose, cellulose acetate and cellulose nimoplasticsto hard cross-linked enamels. Thus, the physitrate. Also, thermosettingresins including phenolic resins;

cal properties of the final photoconductive layer may be amino resinssuch as urea-formaldehyde resins and melamineformaldehyde resins;unsaturated polyester resins; epoxy resins, silicone polymers; alkydresins and furan resins. Various copolymers and mixtures of theabovementioned resins may be used where applicable. In addition to theabove-noted resins, any other suitable material may be used if desired.

The quinacridone compositions of the present invention may beincorporated into the dissolved or melted binderresin by any suitablemeans such as strong shear agitation, preferably with simultaneousgrinding. Typical methods include ball milling, roller milling, sandmilling, ultrasonic agitation, high speed blending and any combinationof these methods. Any suitable ratio of pigment to resin may be used. Ona quinacridone-dry resin weight basis, the useful range extends fromabout 1:1 to about 1:40. {Best results are obtained at, and thereforethe preferred range is, from about 1:4 to about 1:10. Optimum resultsare obtained when the ratio is about 1:4. While highest photosensitivityis obtained at pigment-resin ratios of 1:1 to 1:4, at the highconcentration of pigment dark conductivity increases. The optimumbalance between sensitivity and dark decay occurs at a ratio ofabout1:4. It should be noted that the proportion of photoconductor used inthe preferred range lies substantially below that used in makingheretofore known inorganic photoconductive binder plates. In these knownplates, satisfactory electrophotographic sensitivity is attained onlywhen the pigment-resin ratio is at least 2: 1.

The use in the present invention of lower pigment to resin ratiosrepresents a highly desirable advantage over the prior art since asmaller amount of the relatively expensive pigment component isrequired. Also, this permits very smooth adhesive coatings to beobtained because of the high binder content. The small proportion ofadded material has little efiect on the physical properties of thebinder-resimThus, resins may be chosen having the desired softeningrange, smoothness, hardness, tough: ness, solvent resistance, orsolubility and the like with assurance that the pigment will not affectthese properties to any considerable extent.

When it is desired to coat the quinacridone-resin film on a substrate,various supporting materials may be used. Suitable materials'for thispurpose include aluminum, steel, brass, metallized or tin oxide coatedglass, semiconductive plastics and resins, paper and any otherconvenient material of bulk resistivity at the time of use v ohms-cm.,or surface resistivity -10 ohms/square. The pigment-resin-solvent slurry(or the pigment-resin-melt) may be applied to conductive substrates byany of the wellknown painting or coating methods, including spraying,flow-coating, knife coating, electro-coating, Mayer bar drawdown, dipcoating, reverse roll coating, etc. Spraying in an electric field may bepreferred for smoothest finish and dip coating may be preferred forconvenience in the laboratory. The setting, drying, and/ or curing stepsfor these plates are generally similar to those recommended for films ofthe particular binders'as usedfor other'painting applications. Forexample, quinacridoneepoxy plates may be cured by adding a cross-linkingand stoving according to approximately about the same schedule as otherbaking enamels made with the. same resins photoconductive coating andpreferably should beno more than 4/; the thickness of said coating. Anysuitable overcoating, as for example, nitrocellulose lacquer, may beemployed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following examples willfurther define various preferred embodiments of the present invention.Parts and percentages are by weight unless otherwise specified.

EXAMPLE 1 An electrophotographic plate is prepared by initially mixingabout 6 parts Pliolite 85B, a styrene-butadiene copolymer resinavailable from Goodyear Tire and Rubber Company, about 43 parts xyleneand about 1 part of a quinacridone pigmenthaving the formula:

1 to obtain a homogeneous dispersion. After milling, the

and similar pigments for paint application. A very desirable aspect ofquinacridone compositions is that they are stable against chemicaldecomposition at the temperature normally used for a wide variety ofbake-on enamels, and therefore, may be incorporated in very hard glossyphotoconductive coatings, having surfaces similar to automotive orkitchen appliance resin enamels.

The thickness of the quinacridone-binder films may be varied from about1 to about 100 microns, depending upon the required characteristics.Self-supporting films, for example, cannot be conveniently manufacturedin thickdispersion is applied to a sheet of 5 mil aluminum foil using aNo. 36 wire draw-down rod. The coating is then forced air dried at aboutC. for about two hours. The plateisthen charged to a positive potentialof about 65Q volts by means of corona discharge, as described, forexample, in US. Patent 2,777,957. The charged plate is then contactexposed for 15 seconds to a film positive by means of a tungstenlamp-having a 3400 K. color temperature. The illumination level at theexposure plane is about 57 foot candles. The latent electrostatic imageformed on the plate is then developed by cascadingpigmentedelectroscopic marking particles over the plate, by the processdescribed, for example, in US. Patent 2,618,- 551. The powder imagedeveloped on the plate is electrostatically transferred to a receivingsheet and heat fused thereon. The image on the receiving sheet is ofgood quality and corresponds to the contact exposed original. I

EXAMPLE II rnixingabout 2 parts Silicone SR-82, a methyl-phenyl siliconeresin available from General Electric Company,

about 40 parts xylene, and about 1 part of a quinacnidone pigment havingthe formula:

can onmno@ @am. C H O N \H/ 2 5 (m4 7 H 0 -g;

This plate is positively charged to an initial potential of about 290volts. The image resulting is of satisfactory quality. 7

EXAMPLES III-1V Two electrophotographic plates are prepared by mixingabout 1 part Vinylite VYNS, a copolymer of vinyl chloride and vinylacetate available from Union Carbide Corporation, about 10 parts diethylketone and about 1 part of a quinacridone pigment having the formula:

The plate is coated, cured, charged, exposed and developed as in ExampleI above, however, in Example III, the plate is positively charged to apotential of 480 volts and, in Example IV, the plate is charged to anegative potential of 835 volts. The resulting image is of excellentquality.

EXAMPLES V-VI 40 Two electrophotographic plates are prepared byinitially mixing about 1 part of Vinylite VYNS, about 10 parts dieth-ylketone and about 1 part of a quinacridone pigment having the formula:

0 GHzNH- potential of 630 volts. Good images result. I

EXAMPLES VIP-VIII An electrophotographic plate is prepared by initiallymixing about 1 part Vinylite VYNS, about 10 parts diethyl ketone, andabout 1 part of a quinacridone pigment having the formula:

N l oomcumin OCH;

The plate is coated, cured, charged and developed as in Example 1 above.However, here the plate of Example VII is charged to a positivepotential of 410 volts and the plate of Example VIII is chraged to anegative potential of 605 volts. Excellent images are produced by theseplates.

EXAMPLES IX-X Two electrophotographic plates are prepared by initiallymixing about parts of a 10 percent solution of polyvinyl carbazole inbenzene, about 5 parts cyclohexanone, and about 1 part of thequinacridone pigment of Example I. These plates are coated, cured,charged, exposed and developed as in Example -1 above. However, here theplate of Example ]X is charged to a positive potential of about 180volts and the plate of Example X is charged to a negative potential ofabout 215 volts. Images of good quality are produced.

EXAMPLES XI-XIl Electrophotogranhic plates are prepared by initiallymixing about 100 parts of a 10 peroentpolyviuyl carbazole solution inbenzene, about 5 parts cyclohexanone and about 1 part of thequinacridone pigment of Example II. The plates are coated, cured,charged, exposed and developed as in Example I above. However, here theplate of Example XI is charged to a positive potential of about voltsand the plate of Example XII is charged to a negative potential of aboutvolts. Images of good quality result. 7 I

Although specific components in proportions have been described in theabove examples relating to the use of "a novel class of quinacridonepigments in electrophotographic plates, other suitable materials, aslisted above,

may be used with similar results. In addition, other materials may beadded to the quinacridone pigment compositions or to the pigment-resincompositions to synergize, enhance, or otherwise modify theirproperties. The pigment compositions and/or the pigment-resincompositions of this invention may be dyesensitized, if desired, or maybe mixed or otherwise combined with other photoconductors, both organicand inorganic.

Other modifications and ramifications of the present invention willoccur to those skilled in the art upon a reading of the presentdisclosure. These are intended to be included within the scope of thisinvention.

What is claimed is:

1. An electrophotographic imaging process which comprises uniformlycharging the surface of an electrophotographic plate comprising aself-supporting layer of an electrophotographic composition comprising aphotoconductive quinacridone pigment in a binder material, saidquinacridone pigment having the formula:

wherein R is selected from at least one member of the group consistingof CH C H OCH OC H and a halogen and wherein R is selected from at leastone member of the group consisting of an aromatic group, a heterocyclicgroup, an alicyclic group and an aliphatic group, said layer having athickness greater than about microns, and exposing said charged plate toa pattern of activating electromagnetic radiation to produce anelectrostatic latent image.

2. An electrophotographic imaging process which comprises uniformlycharging the surface of an electrophotographic plate comprising asupport substrate having a bulk resistivity greater than about 10+ohms-centimeter having superimposed thereon a photoconductive layer 0 llH E wherein R is selected from at least one member of the groupconsisting of CH, C H OCH, OC H and a halogen and wherein R is selectedfrom one member of the group consisting of an aromatic group, aheterocyclic group, an alicyclic group and an aliphatic group, andselectively exposing said charged plate to activating electromagneticradiation to produce an electrostatic latent image.

3. The process as disclosed in claim 1 further including the steps ofdeveloping said latent image with electroscopic marking particles.

4. The process as disclosed in claim 2 further including the step ofdeveloping said latent image with electroscopic marking particles.

5. The process as disclosed in claim 3 wherein the imaging cycle ofcharging, exposing and developing is repeated at least once.

6. The process as disclosed in claim 4 wherein the imaging cycle ofcharging, exposing and developing is repeated at least one time.

References Cited UNITED STATES PATENTS 3,074,950 1/1963 Deuschel et al.260279 3,121,006 2/1964 Middleton et al. 961

3,384,566 5/1968 Clark 201-181 3,386,843 6/1968 Jaife et al 106-288FOREIGN PATENTS 1,085,680 10/1967 Great Britain.

GEORGE F. LESMES, Primary Examiner J. C. COOPER llll, Assistant ExaminerUS. Cl. X.R. 96---l.5

